These efforts cover both basic and applied aspects of mycoplasmas and related wall-free prokaryotes (mollicutes), including their molecular biology, membrane and cellular components involved in attachment, virulence, or immunological interrelationships, and their possible role in human disease or diseases of uncertain etiology. Current efforts involve the characterization of a group of sterol non-requiring mollicutes (genus Acholeplasma) isolated from variety of human tissue sites and from other environmental origins. A strain of Acholeplasma oculi has been identified in the amniotic fluid of a patient undergoing aminocentesis, and a strain of Acholeplasma laidlawii has been identified in the tissues of a stillborn infant. We have also characterized ten other acholeplasmas recovered from a variety of insect and plant origins. Most of these mollicutes have been found to be serologically distinct from all other acholeplasmas, but have the general features (no serum requirement for growth, genome size of 1 x 1\billion daltons, G+C value of 30-35 mole%, etc.) of acholeplasmas. Further efforts to understand the ecology of these mollicutes and their occurrence in human tissues appears justified. Additional work on identification of the attachment protein in Mycoplasma genitalium suggests that a 143 K protein is involved in adherence of the organism to human tissues, and this protein can be separated from the 165 K protein (P1) identified as the main attachment moiety in Mycoplasma pneumoniae. Antibody to the 143 K protein has been identified in the serum of chimpanzees following an experimental genital tract challenge with Mycoplasma genitalium.